Fabrication of ultra-sharp (i.e., nanometer-sharp and atomically sharp) tips is among the most important prerequisites for producing coherent and bright particle beams (i.e., electron or ion beams) and obtaining valuable information from scanning beam/probe microscopes. The spot size of the particle beam, which depends on the sharpness of the tip, defines the lateral resolution of the microscope. Therefore, an ideal particle beam will be the one originated from a single-atom tip (“SAT”) with minimum energy spread and opening angle.
Although tips with atomic sharpness (i.e., a tip formed of a single atom or less than 15 atoms) are highly desirable as they greatly improve the resolution of the microscope, they are difficult to prepare. Conventional methods for preparing single-atom tips in general require special equipments and complicated procedures. For example, a field ion microscope (FIM) or field emission microscope (FEM) is indispensable to monitor the tip in situ so that when the tip reaches its sharpest state (e.g., single-atom sharpness), one can stop the process to prevent the tip from turning blunt again. In addition, tips so prepared are usually not stable thus have short operation lifetimes. Tungsten is frequently used as a material for preparing the single-atom tips. However, at high fields, the tungsten tips will be corroded by chemically active ions such as O2+, N2+, H2O+, which greatly shorten their lifespan. Further, most of the ultra-sharp tips prepared by traditional methods cannot be regenerated.
These drawbacks hinder the ultra-sharp tips from commercial applications. They have so far only been used in the research laboratories. There is a need for stable, regenerable atomically sharp tips, especially single-atom tips and simple, reliable, low-cost methods for preparing them.